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Couple switch not working due to wrong SMD component

Posted: Mon Jan 23, 2023 9:57 pm
by Dominic

I purchased and assembled two DSO Shell DIY Kits.
Both of them are 15001K kits with pre-assembled SMD parts.

The first one works correctly, but for the second one, during assembly step 4 (Check Voltages), the value for AV+ on the analogue board was incorrect.
In the user interface, the couple switch does not switch through all three positions correctly.

I compared all components I assembled with the components of the other kit that works correctly.
Swapping the analogue board between the two kits helped me to identify that there was a problem with one analogue board.

I investigated further and measured the built-in component values.
Doing that, I noticed that in the place of U4, a 79L05, instead of a 78L05, was pre-assembled.

The question I now have is, can I replace the wrong 79L05 with the correct 78L05 and assume that the board will then work correctly?
I am asking because I wonder if the already powered board with the wrong regulator may have damaged other components.

I also looked at the pre-assembled SMD part list for the analogue board.
All capacitors on the analogue board list are of the same value, and when I looked on the board, they all looked equal, which should be correct.
The resistors R18, R17, R19, and R20 match with the correct working board.

I am attaching several pictures of the boards and hope the wrong component can be seen correctly.
The not working analogue board is on the left.
It is the one that is not yet assembled in the case.

Thanks for the advice.

Best Regards,